A damping valve capable of adjusting a damping force is, for example, used by being built into a damper of a front fork of a two-wheel vehicle.
JP2008-14431A discloses a damper including a cylinder coupled to an outer tube, a piston slidably inserted into the cylinder to partition the interior of the cylinder into a compression side chamber and an expansion side chamber, a piston rod inserted into the cylinder and having one end coupled to an inner tube slidably inserted into the outer tube and the other end coupled to the piston, a communication path allowing communication between the compression side chamber and the expansion side chamber, and a check valve provided at an intermediate position of the communication path and permitting only a flow from the compression side chamber toward the expansion side chamber or a flow from the expansion side chamber toward the compression side chamber. A damping valve used in this damper includes an annular valve seat provided at an intermediate position of the communication path, a needle-like valve body to be seated on and lifted from the valve seat and a stepping motor fixed to the other end side of the piston rod for driving the valve body.
This damper exerts a damping force by applying resistance to the flow of hydraulic oil by a piston valve provided in the piston during expansion and exerts a damping force by applying resistance to the flow of hydraulic oil flowing out from the cylinder to a reservoir by a base valve provided at an end part of the cylinder during contraction.
Further, in this damper, the hydraulic oil flows in the communication path only during expansion or during contraction by the action of the check valve and a damping force is exerted by applying resistance to this flow of the hydraulic oil by the valve body. The damping valve also cooperates to exert a damping force during either one of the expansion and the contraction of the damper. The flow passage area of the damping valve is adjusted by driving the valve body by the motor, thereby making the damping force of the damper variable.
That is, the damping valve fulfills a damping function only during the expansion or the contraction of the damper. However, since a pair of left and right front forks normally suspend a wheel of the two-wheel vehicle, the left and right front forks can adjust damping forces at an expansion side and a contraction side as a whole by causing the valve body of the damper built in one front fork to fulfill the damping function during expansion and causing a needle valve of the damper built in the other front fork to fulfill the damping function during the contraction.